According to the art, halogenated 1,3-dioxolanes are prepared starting from complex reagents or using industrially onerous multistage processes, which provide often low or not constant yields, as is better explained later on.
German patent application No. 2,604,350 teaches the synthesis of halogenated 1,3-dioxolanes by fluorination of the corresponding ethylcarbonate with SF.sub.4 +HF (or TiF.sub.4).
Published European patent application No. 80,187 describes the synthesis of perfluoro-1,3-dioxole and of its polymers via dechlorination of the corresponding 4,5-dichloro-dioxolane, prepared starting from ethylene carbonate by photochemical chlorination with Cl.sub.2 and subsequent fluorination with SF.sub.4 +HF and with SbF.sub.3 (or HF)+SbCl.sub.5 ; The yields of said last step can also be greater than 90%, but they are not reproducible.
The abovesaid 4,5-dichlorodioxolane is also prepared from 1,3-dioxolane by photochemical chlorination with Cl.sub.2 and fluorination with SbF.sub.3 (or HF)+SbCl.sub.5 ; However, the total yield does not exceed 7%.
U.S. Pat. No. 2,925,424 describes how to synthesize halogenated 1,3-dioxolanes by reacting a perhaloketone with a 2-haloethanol.
In U.S. Pat. Nos. 3,865,845 and 3,978,030, fluorinated dioxoles and homopolymers and copolymers thereof are prepared by dehalogenizing dioxolanes with two vicinal halogens, prepared according to the method described in the above-cited U.S. Pat. No. 2,925,424.
European patent applications Nos. 76,581 and 301,881 describe the condensation of a fluorinated ketoester with a 2-haloethanol or an ethylene oxide in order to obtain halogenated 1,3-dioxolanes.
U.S. Pat. No. 3,699,145 describes the photo-oxidation of perfluoropropene with molecular oxygen whereby it is possible to obtain, along with various straight perfluoropolyethers, low amounts of perfluoro-4-methyl-1,3-dioxolane and of perfluoro-2,4-dimethyl-1,3-dioxolane.
In Journal of Fluorine Chemistry 12 (1978), pages 23-29, the reaction of bis(fluoroxy-difluoromethane with the Dewar hexafluorobenzene is described. It is expressly stated that, although the perfluorocycloolefins are generally not reactive towards bis(fluoroxy)difluoromethane, in the case of the Dewar hexafluorobenzene, along with polymeric products, oxiranic products and products resulting from a simple fluorination of the double bond, there are obtained, with low yields, products having a dioxolane structure. The higher reactivity is attributable to its particular dicyclic structure, which exhibits olefinic bonds with anomalous angles.
Lastly, Organic Chemistry 3 (1986), 624-6, describes the reaction of bis(fluoroxy)difluoromethane (hereinafter briefly referred to as "BDM") with two particular olefins: tetrafluoroethylene and trans-1,2-dichloroethylene.
When it is operated with tetrafluoroethylene, a mixture of the olefin, diluted in a nitrogen excess, is fed to BDM at a temperature of -184.degree. C.; at said temperature, the reagents are in the solid state. Alternatively, the olefin and the BDM are condensed together in the reaction vessel at -184.degree. C. In both cases, not the corresponding 1,3-dioxolane but the addition product of formula CF.sub.2 (OCF.sub.2 --CF.sub.3).sub.2 is obtained.
In the reaction with trans-1,2-dichloroethylene it is operated, according to the above-cited article, by condensing the olefin with a solvent and the BDM in the reaction vessel at a temperature of -184.degree. C. and then allowing the whole to stand for a few days at room temperature. Also in this case, not the corresponding 1,3-dioxolane, but the straight compound of formula CF.sub.2 (OCH--CHClF).sub.2 is obtained.
Thus, from the examined art, it is apparent that up to the date of the present invention it was not known to prepare 1,3-dioxolanes by direct reaction of olefins with bis(fluoroxy)perfluoroalkanes, and only a limited number of halogenated 1,3-dioxolanes could be prepared by means of complicated processes and with not always satisfactory and reproducible yields.